Kinetics

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Rate of Reaction

The speed at which the reactants disappear and products are formed.

CONCENTRATION AND PRESSURE

Higher concentration and pressure will result in a faster rate of reaction due to more collisions. 

TEMPERATURE

Higher temperature increases the average energy of each partical so faster movement results in more collisions. 

SURFACE AREA

If the surface area of a solid is increased, rate of reaction is increased. 

Homogenous reactions - reactants are in the same phase 

Heterogenous reactions - reactants are in different phases

CATALYSTS

Changes the rate of reaction without undergoing any permanent change.

Speed up rate of reaction, by lowering activation energy. 

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Measuring rates of reactions

Rate of reaction = change in concentration / change in time

Measuring volume of gas - counting the number of bubbles at regular time intervals. 

Measuring the change of mass in the reactant mixture - measure the mass of the total reaction mixture as the reaction progresses, and see how quickly it decreases. 

Monitoring colour change - e.g. iodine reaction. Measure how fast it takes to turn blue/black

Other methods include:

  • Titrimetric analysis
  • Colorimetirc analysis
  • Conductimetric analysis 
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Activation Energy

In order for particles to react they must collide with certain minimum kinetic energy. 

If two slow moving particles collide, they will simply bounce apart as a result of repulsion.

(http://cimg1.ck12.org/datastreams/f-d%3Adf0a2687d885c997ec852a60b09181c51b0a234ada9136e0288d4e8c%2BIMAGE%2BIMAGE.1)

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Initial Rate

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Maxwell-Boltzmann distribution

As temperature rises, the graph flattens as activation energy lowers. The particles are moving fast enough to overcome activation energy. 

(http://www.chemistry.wustl.edu/~edudev/LabTutorials/Airbags/images/maxwell.jpg)

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Rate of Reaction cont.

SURFACE AREA

If the surface area of a solid is increased, rate of reaction is increased. 

Homogenous reactions - reactants are in the same phase 

Heterogenous reactions - reactants are in different phases

CATALYSTS

Changes the rate of reaction without undergoing any permanent change.

Speed up rate of reaction, by lowering activation energy. 

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